A screw extruder housing of this kind is known, for example, from FIG. 1 of German Gebrauchmuster No. 7,320,419, in which each of two interconnected bores has a wear insert made of a thin-walled bimetal tube. For this purpose each bimetal tube has a portion milled away. After this portion has been milled away, the two tubes are either inserted singly into the casing and welded or pinned to the latter, or before insertion into the casing are welded together at their contact surfaces in the region of the saddles, i.e. the region at which the walls of the bores meet.
Furthermore, it is known, for example, from U.S. Pat. No. 3,900,188 to make a screw extruder housing from a normally solid material and to solder in position an inserted wearing sleeve. In addition, it is known for wearing sleeves of this kind to be shrunk into position.
Moreover, it is known for screw extruder housings to be made of a special solid material and for the walls of the bores to be hardened by nitriding, case hardening, boriding, or ionitriding. It is likewise known to make screw extruder housings of this kind from individual tubes whose inner walls are coated with a wear-resistant layer of metal or metal oxide powders applied by centrifuging. It is also known to produce a wearing coating by hard chromium-plating, hard nickel-plating or spraying with metal oxide powders. In the case of spraying with metal oxide powders, ceramic powders are in some cases used as binders with low-melting metal powders.
In all these known screw extruder housings provided with protection against wear, the production of the wear-resistant lining or coating protecting against wear on the walls of the bores entails heavy expense for production, while in addition wear-resistance still leaves much to be desired.
From German Gebrauchmuster No. 1,943,626 it is known for grooves to be provided in the region of the so-called saddle points in a worm casing having two axially parallel interconnected bores, and to insert in these bores special saddle elements which on their surfaces coming into contact with the material being processed are strengthened with media protecting against wear, these saddle elements being adapted to be tightened from outside by means of clamp screws and pressing the wearing bushes, with prestressing, uniformly firmly and tightly against the cylinder casing.